This invention relates to a spiral or helical brush section adapted to be used in multiples of axially-interfitting or nesting sections to complete a rotary brush of desired length. Continuous spiral brushes are now commonly made in the form of a one-piece elongated drum having the brush bristles mounted thereon as a continuous helix or spiral extending from one end of the mandrel to the other. This type of brush is ordinarily employed in removal from and replacement on a drive mandrel because of its weight due to the one-piece drum construction. Attempts have been made in the prior art to overcome this by making the brush in short spiral sections, but the arrangements provided leave large gaps in the spiral where the sections abut. Another arrangement in an attempt to overcome this is the use of rings or wafers of bristles mounted on the mandrel but this is not a spiral which is desirable.